Palynological delimitation of the lower gondwanas in the north Karanpura sedimentary basin, India

Abstract

The Lower Gondwana outcrops exposed in the North Karanpura sedimentary basin comprise Talchir, Karharbari, Barakar, Barren Measures and Raniganj formations. A lot of surface and subsurface samples have been palynologically investigated from all these formations. It has been observed that in Talchir, the assemblage is dominated by monosaccates. The Lower Karharbari is dominated by triletes followed by monosaccates while in the Upper Karharbari monosaccates are dominant and bisaccates are next in abundance. In the Lower Barakar, the assemblage is dominated by striate bisaccates and monosaccates are found in small percentage. The next palynological zone in Barakar is dominated by triletes where there are thick coal seams. In the Upper Barakar, triletes dwindle down and striate bisaccates predominate. The Barren Measures is also dominated by striate bisaccates but presence of a monosaccate genus viz. Densipollenites in good percentage easily distinguishes this formation from the upper and lower ones. In the Raniganj, striate bisaccates are in abundance and where there are thick coal seams, triletes and monoletes are found in appreciable percentage. Eight palynological zones have been established. It is observed that the various formations of the Lower Gondwanas in the North Karanpura sedimentary basin can be demarcated by means of palynological fossils. The relative dominance or paucity of triletes, monosaccates and bisaccates can be effectively used for demarcation of the various formations. It is observed that change in palynological assemblage from one formation to another is gradual and the palynological demarcation exactly between the uppermost and lowermost parts of the two successive formations based on lithology is rather difficult. After this transitional zone, the palynological assemblage gradually differs from one another and thus palynological boundary between the two formations can be marked satisfactorily.